I'm trying to get our 240DL through the state dept of Environmental Quality test, but the tester says the engine idle is too high. I've looked in the manual and cannot find an idle adjustment screw for this model? Any help on this one?

 

There isn't one.

Try cleaning the throttle body.

Did he say what the idle was at?

 

Yeah it is about 1100-1200 so it is fast. I'm guessing it should be in the 750-800 level, correct?

I'll check the book for the throttle body...

 

Yes that is to high and yes it should be about 750 or so.
Don't try adjusting the throttle blade. That is unless you remove the throttle body and clean it.
Also make sure someone didn't adjust the rod to make it idle.